Willa of Dark Hollow by Robert Beatty 

The Great Smoky Mountains. 1901. Willa and her clan are the last of the Faeran, an ancient race of forest people who have lived in the mountains for as long as the trees have grown there. But as crews of newly arrived humans start cutting down great swaths of the forest she loves, Willa is helpless to stop them. How can she fight the destroyers of the forest and their powerful machines? When Willa discovers a mysterious dark hollow filled with strange and beautiful creatures, she comes to realize that it contains a terrifying force. Is unleashing these dangerous spirits the key to stopping the loggers? … Read more.